Energy harvesting from ambient sources has become a topic of interest for increasing the lifetime of electronic devices, especially in wireless sensor nodes. In addition, energy harvesting can recharge batteries to prolong the life of electronic devices, in some cases enabling devices to run perpetually without human intervention. Thus, such techniques are useful in hard to reach places such as bridges and in implants such as pacemakers.
Energy can be harvested from many sources such as solar, thermal, vibration and RF. The availability of these sources affect the life time of the electronic device that use them. Further, in some energy source such as thermal, the availability depends on the polarity of the source. As such, detecting the polarity of the energy source is indeed necessary for perpetual operation of the electronic devices. For example, thermal energy harvesting is conventionally done by converting thermal energy into electrical energy using a thermoelectric generator (TEG). When a temperature difference exists across a TEG, an electron-hole pair moves inside the TEG thereby producing a current flow. This phenomenon is called the Seebeck effect. The amount of output voltage is related to the temperature difference across the TEG. The polarity of the output voltage depends on the orientation of the TEG relative to the hot and cold temperature reservoirs.